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J. Biol. Chem., Vol. 262, Issue 3, 1105-1110, 01, 1987
ML MacDonald, KF Mack and JA Glomset
The regulation of phosphoinositide phosphorylation was studied in Swiss 3T3
cells that were stimulated by platelet-derived growth factor (PDGF).
Studies with intact cells showed that the mitogen increased the
incorporation of 32P into phosphatidylinositol (PtdIns),
phosphatidylinositol 4-phosphate (PtdIns-P), and phosphatidylinositol
4,5-bisphosphate (PtdIns-P2) during the cell cycle, with distinct peaks of
incorporation for all three phosphoinositides after 1 h, and for PtdIns and
PtdIns-P2 after 20 h. Direct measurements of the activities of PtdIns
kinase and PtdIns-P kinase in freeze-thawed cells revealed that the
activity of PtdIns kinase was rate-limiting for the synthesis of PtdIns-P2.
Maximal activities of PtdIns kinase and PtdIns-P kinase, with exogenous
substrates, were unchanged during the 1st h of PDGF treatment, but doubled
during the next 24 h. The increase in PtdIns kinase activity began within
2-4 h, exceeded the increase in cell protein, and was abolished by
cycloheximide, which suggests that the enzyme was induced specifically in
response to PDGF. The increase in activity of PtdIns-P kinase paralleled
the increase in cell protein. Dose-response curves for PDGF showed that the
activities of PtdIns kinase and PtdIns-P kinase at 24 h increased in
proportion to the extent of mitogenic stimulation of the cells. Our results
support the conclusion that the activities of PtdIns kinase and PtdIns-P
kinase increase in response to PDGF, but only after several hours of cell
cycle traverse.
Regulation of phosphoinositide phosphorylation in Swiss 3T3 cells stimulated by platelet-derived growth factor
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